Head-group-influenced mixed micellization of sodium deoxycholate with conventional hydrocarbon surfactants of identical hydrocarbon tails

Conductivity, viscosity, turbidity, and NMR measurements were performed over most of the mole fraction range for sodium deoxycholate (SDC) with hexadecyltrimethylammonium bromide (HTAB), hexadecylpyridinium bromide (HPyBr), and hexadecylpyridinium chloride (HPyCl). All studies demonstrate that the mixed-micelle formation is more favorable in SDC plus HTAB rather than SDC plus HPyBr or SDC plus HPyCl mixtures. The results showed that the bulky pyridinium head groups of HPyBr or HPyCl create steric incompatibility with rigid SDC monomers in the mixed state.     

Order and chaos in soft condensed matter

Soft matter, like colloidal suspensions and surfactant gels, exhibit strong response to modest external perturbations. This paper reviews our recent experiments on the nonlinear flow behaviour of surfactant worm-like micellar gels. A rich dynamic behaviour exhibiting regular, quasi-periodic, intermittency and chaos is observed. In particular, we have shown experimentally that the route to chaos is via Type-II intermittency in shear thinning worm-like micellar solution of cetyltrimethylammonium tosylate where the strength of flow-concentration coupling is tuned by the addition of sodium chloride. A Poincaré first return map of the time series and the probability distribution of laminar length between burst events show that our data are consistent with Type-II intermittency. The existence of a ‘Butterfly’ intensity pattern in small angle light scattering (SALS) measurements performed simultaneously with the rheological measurements confirms the coupling of flow to concentration fluctuations in the system under study. The scattered depolarised intensity in SALS, sensitive to orientational order fluctuations, shows the same time-dependence (like intermittency) as that of shear stress.     

Studies in oxidation-reduction reactions: Oxidation with chloramine-b indirect determinations

Chloramine-B has been used as an oxidizing agent in hydrochloric acid medium for the indirect volumetric estimations of hydrogen peroxide, lead dioxide, manganese dioxide, selenium dioxide, sodium formate, sodium sulphide, sodium metavanadate, potassium iodate and copper sulphate using iodine monochloride as a catalyst and pre-oxidiser. Chloroform is used as an indicator. It is coloured pink owing to the liberation of iodine during the titration and becomes light pale yellow at the end-point because of the formation of iodine monochloride.     

Vaporization thermodynamics of thorium tetrafluoride

The thermal decomposition kinetics of Pr₂(SO₄)₃ to Pr₂O₂SO₄ have been studied by isothermal weight change determination. The reaction was found to obey a linear law up to α = 0.5; beyond α = 0.5 it could be described as a phase-boundary controlled process. A dependence of the activation energy upon the sample weight was observed. The changes in surface area and density which occur during the decomposition are also given.     

Volumetric studies in oxidation-reduction reactions: Oxidation with chloramine-t. iodine monochloride method

Chloramine-T has been used as an oxidizing agent in hydrochloric acid medium' for the volumetric estimations of potassium iodide, hydrazine sulphate, arscnious oxide, stannous chloride, mercurous chloride, tartar-emetic, potassium thiocyanate and ferrous ammonium sulphate, using iodine monochloride as a catalyst and pre-oxidizer. Chloroform is used as an indicator. It is coloured pink owing to the liberation of iodine during the titration and becomes very pale yellow at the end-point because of the formation of iodine monochloride.